1. Field of the Invention
This invention relates to a continuous process for the preparation of phthalic esters of saturated alcohols wherein the waste streams obtained in the process are purified so as to permit recycling of organic by-products and unreacted components to the process.
2. Description of the Prior Art
Continuous processes for the production of phthalic esters from saturated alcohols are known in the prior art. Recycling of the monoester by-product obtained by extraction of the product of the esterification utilizing the same alcohol used for the esterification is disclosed by Suter et al in U.S. Pat. No. 3,886,199. However, it has been found that, where the monoester is recycled, discoloration of the desired diester product occurs, especially where process conversion to the diester is about 90 to about 98 percent. In U.S. Pat. No. 3,896,159, Kratzer et al, there is disclosed an improvement in the process of preparing phthalic esters from saturated alcohols wherein a substantial reduction in the waste water discharged from the process is obtained by the utilization in the process of water generated in the esterification reaction thus reducing the amount of waste water by about 75 percent of the original amount produced in a conventional process. Helgorsky et al in U.S. Pat. No. 3,933,630 disclose a critical free-acidity is necessary for the desired purification of an acidified water phase obtained subsequent to neutralization of the reaction product of the esterification in a process for the production of phthalic esters. This permits the acidified water phase to be subsequently extracted with the same alcohol used in the esterification process and, without further purification, recycled to the esterification process.
Recently, in U.S. Pat. No. 4,066,835 to Hahn et al, there is disclosed a process for the purification of waste water produced in the process of producing diester plasticizer such as dioctyl phthalate wherein organic components in the waste water produced in the process are removed and subsequently recycled to the esterification process by heating the aqueous phase obtained subsequent to separation of the diester reaction product. The process consists of heat treating said aqueous phase to a temperature of above 200.degree. C. under the appropriate pressure to form an organic phase and an aqueous phase, the organic phase is then removed and recycled to the process. The recycled organic phase does not disadvantageously affect the production of the ester or detract from the quality of the ester produced. The remaining aqueous phase is then readily purified so as to meet environmental standards.
In no one of the references cited, is a process disclosed for the production of phthalic esters wherein both organic and inorganic impurities are removed from the desired reaction product utilizing conventional process steps and recycled to the process. The recycle to the process of all organic waste products and all waste water produced in the process is not disclosed in the prior art.